This invention relates to a charge control microcomputer for a vehicle, which externally determines a voltage control value which is used to control the output voltage of a charging generator driven by an internal combustion engine of a vehicle or the like.
In general, in a conventional device of this type, the output voltage of a generator driven by an internal combustion engine or the like is controlled to a predetermined value which is preset by the voltage regulator installed together with the generator. The output voltage thus controlled charges the vehicle battery. The voltage regulator generally has a temperature compensation characteristic, and the predetermined value thereof is affected by the ambient temperature. That is, the predetermined value is decreased with increasing temperature at a preset negative temperature gradient, so that it is relatively corrected for the battery's charging characteristic temperature gradient.
The generator is installed directly on the engine, while the battery is located on the body side of the engine compartment, and at a corner which is less affected by the engine heat. That is, the generator and the battery are different from each other in their installation locations. In addition, the voltage regulator is much different from the battery in thermal capacity. Therefore, in many cases, it is difficult to maintain the correlation in temperature increase between the voltage regulator and the battery. Thus, the conventional device suffers from a drawback in that it is difficult to effectively correct for the battery's changing charging characteristic according to the temperature increase.
The internal resistance of the battery changes when used for a long time. Accordingly, with a preset temperature compensation characteristic, it is difficult to maintain a predetermined voltage value best for the travelling pattern of the vehicle.